linux-kernel - Re: [PATCH 2/6] irq_work: Implement remote queueing

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Message-ID: <53AA9B68.4050104@linux.vnet.ibm.com>
Date:	Wed, 25 Jun 2014 15:20:32 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH 2/6] irq_work: Implement remote queueing

On 06/25/2014 03:09 PM, Peter Zijlstra wrote:
> On Wed, Jun 25, 2014 at 11:36:57AM +0200, Peter Zijlstra wrote:
>> On Wed, Jun 25, 2014 at 12:07:05PM +0530, Srivatsa S. Bhat wrote:
>>> I don't think irqs_disabled() is the problematic condition, since
>>> hotplug_cfg() invokes irq_work_run() from CPU_DYING context (which has
>>> irqs disabled). I guess you meant to remove the in_irq() check inside
>>> irq_work_run() instead?
>>
>> Yes, clearly I should not get up at 6am.. :-) Let me go do a new one.
> 
> ---
> Subject: irq_work: Remove BUG_ON in irq_work_run()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Jun 25 07:13:07 CEST 2014
> 
> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
> pending IPI callbacks before CPU offline"), which ends up calling
> hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
> is not from IRQ context.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Reported-by: Stephen Warren <swarren@...dotorg.org>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Link: http://lkml.kernel.org/n/tip-busatzs2gvz4v62258agipuf@git.kernel.org
> ---
>  kernel/irq_work.c |   12 +-----------
>  1 file changed, 1 insertion(+), 11 deletions(-)
> 
> Index: linux-2.6/kernel/irq_work.c
> ===================================================================
> --- linux-2.6.orig/kernel/irq_work.c
> +++ linux-2.6/kernel/irq_work.c
> @@ -160,21 +160,11 @@ static void irq_work_run_list(struct lli
>  	}
>  }
> 
> -static void __irq_work_run(void)

Hmm, irq_work_cpu_notify() calls __irq_work_run() in the CPU_DYING
phase, to by-pass BUG_ON(!in_irq()). How about doing the same thing
from hotplug_cfd() as well?

> +static void irq_work_run(void)
>  {
>  	irq_work_run_list(&__get_cpu_var(raised_list));
>  	irq_work_run_list(&__get_cpu_var(lazy_list));
>  }
> -
> -/*
> - * Run the irq_work entries on this cpu. Requires to be ran from hardirq
> - * context with local IRQs disabled.
> - */
> -void irq_work_run(void)
> -{
> -	BUG_ON(!in_irq());
> -	__irq_work_run();
> -}
>  EXPORT_SYMBOL_GPL(irq_work_run);
> 
>  /*
> 

Regards,
Srivatsa S. Bhat

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